Flashcards in DR: canine pyoderma Deck (51)
3 types of pyoderma
surface, superficial and deep
Describe surface and superficial pyodermas
epidermis only, don't penetrate below BM. typically exudative. lesions include papules, pustules, epidermal collarettes, scales, crusts, often pruritus.
Describe deep pyoderma
penetrate below BM into dermis and depper tissues, lesions include haemorrhagic bullae, nodules, ulcers, draining tracts (haemorrhagic or purulent discharge)
How is pyoderma diagnosed? 5 types?
problem-based classification based on lesion appearance:
- SEBORRHOEIC PYODERMA - erythema, erosions, exudation without pustules and collarettes
- PAPULES, PUSTULES, SCALE, FOCAL ALOPECIA
- EROSIONS and/or ULCERS
- ULCERS AND DRAINING SINUS TRACTS
- NODULES and/or REGIONAL SWELLING
Name 2 causes of seborrhoeic pyodermas - erythema, erosion, exudation without pustules and collarettes
- bacterial overgrowth syndrome
Name 3 causes of PAPULES, PUSTULES, SCALE and FOCAL ALOPECIA
- impetigo (epidermal pustules not centered on hair follicle)
- bacterial folliculitis (commonest cause of canine pyoderma)
- superficial seasonal pyoderma
Name 3 causes of EROSIONS and/or ulcers
- pyotraumatic dermatitis
- intertrigo (severe cases)
- mucocutaneous pyoderma (GSDs)
What causes the ULCERS and DRAINING SINUS TRACT form of pyoderma?
- Furunculosis (deep pyoderma) = associated with rupture of hair follicles, contents spill into dermis, creates FB reaction in dermis or subcutis. Localised or widespread
What is feline chin acne?
a type of furunculosis (i.e. depp pyoderma) with ULCERS and DRAINING SINUS TRACTS. it is a keratinisation disorder associated with comedones and furuncle formation.
What may cause the NODULE and/or REGIONAL SWELLING form of canine pyoderma?
- cellulitis (diffuse infection and inflammation along tissue planes)
What is necrostising fasciitis?
a rare but severe form of cellulitis associated with dissemination of bacterial toxins
How is pyoderma diagnosed?
- CS highly suggestive
- confirmed with cytology
- and where necessary bacterial culture and AB sensitivity
What are the 4 main cytological techniques for diagnosing canine pyoderma?
- adhesive tape strip cytology
- direct impression smears
- indirect impression smears
- needle cores and FNAs
What is adhesive tape strip cytology good for?
- removes outer SC layer and adherent microorganisms
- sample dry, greasy, scaling or eroded lesions
- irregular surfaces or restricted sites
When are impression smears useful?
- moist or seborrhoiec lesions
- direct - erosion, crust underside or ruptured pustule
- indirect - when slide cannot be apposed to skin and adhesive tape strips are unsuitable (use cotton bud etc)
When are needle cores useful?
- cutaneous massess and enlarged LNs
How are cytology samples stained?
- Diff-Quik (inflammatory cells and microorganisms
- heat fixation not necessary
- Gram and Ziehl-Nielsen (more precisely ID bacteria_
Describe inflammatory cells in canine pyoderma
- neutrophils predominate in most cases
- degenerate/toxic indicate infection
- non-degenerate (sterile inflammation)
- both may be seen
- macrophages + microorganisms, degnerate cells, other debris suggest chronic and/or deep pyoderma
- many macrophages or MNGCs - mycobacterial or fungal infection
- most inflammatory reactions have moderate lymphocytes, PCs and eosinophils - little diagnostic significance
What is bacterial overgrowth like on cytology?
large numbers of bacteria, often several different forms, with no or only minimal numbers of inflammatory cells
Is the presence of intracytoplasmic bacteria a definite indicator of infection?
Name common rod bacteria
Psuedomonas, Proteus and coliforms
What are potential mistakes in cytology interpretation?
- representative lesions
- don't make diagnosis on signle finding
- positive findings useful
- negative results interpreted with case
When is empirical AB therapy appropriate?
WHEN ALL OF FOLLOWING APPLY:
- non-life threatening infection
- 1st episode of skin infection
- lesions consistent with surface/superficial pyoderma
- cytology consistent with staph infection
- no reason to suspect AB resistance
When is bacterial C+S appropriate?
WHEN ANY OF THE FOLLOWING APPLY:
- life threatening infections
- clinical lesions consistent with deep pyoderma
- CS and cytology not consistent with each other
- rod bacteria seen on cytology (their AB sensitivity is not predictable and may be limited)
- empirical AB tx doesn't resolve infection
- where AB resistance more likely (after one or more BS AB courses, non-healing wounds, postop and other nosocomial infections OR the owner or animal has recent healthcare contacts)
Does cytology or culture yield quantitative data?
cytology - also informs of whether organisms have been phagocytosed and relationship to cutaneous cells and structures
When should you take a sample for cytology if ABs have already been used?
48 hours after last dose of oral ABs or beyond appropriate dose interval for parenteral ABs. If not possible use prolonged and/or enriched cultures
What are the best bacteriology swabs for routine clinical use?
standard cotton tipped swabs in transport medium for aerobic and anaerobic growhth
When are biopsies preferred to swabs?
for deeper lesions as bacteria on skin surface may not be representative of deeper organisms
- local anaesthesia may be bactericidal so may be better to use a ring block, local nn block or GA
What is the proper name for disc diffusion test culture?
Kirby-Bauer disc diffusion tests (use AB impregnated discs) - .n.b. some disc diffusion tests may give misleading results for susceptibility in vitro versus in vivo